Cyanoisothiazolyl bis (thiobenzothiazoles)

ABSTRACT

Cyanoisothiazolyl bis(2-thiobenzothiazoles) of the formula   WHEREIN X IS ONE OR TWO WHICH ARE USEFUL FOR ACCELERATING THE VULCANIZATION OF RUBBER.

Umted States Patent 11 1 1111 3,895,019

DAmico July 15, 1975 CYANOISOTHIAZOLYL BIS (THIOBENZOTHIAZOLES) PrimaryExaminer-Richard J. Gallagher [75] Inventor: John Joseph DAmico, St.Louis,

Mo [57] ABSTRACT [73] Assigneez Monsanto Company St Louis MoCyanoisothiazolyl bis(2-thiobenzothiazoles) of the formula [22] Filed:Aug. 16, 1974 S 21 Appl. N6; 498,051 @i C(S) xc N 5 Related U.S.Application Data N/ il fi [62] Division Of Ser. N0. 351,143, April 16,1973, Pat. x

wherein x is one or two which are useful for accelerat- [52] U.S. Cl.260/306.5; 260/306.6 R ing the vulcanization of rubber. [51] Int. ClC07d 99/02 58 Field of Search 260/3065, 306.6 R 3 Clams DrawmgsCYANOISOTHIAZOLYL BIS (THlOBENZOTl-IIAZOLES) 1 have discovered a classof compounds of the formula S (s) c ii s nc-ll due) ci m wherein x is lor 2 which accelerate the vulcanization of rubber and where x is two,function as primary vulcanizing agent useful as the sole vulcanizingagent or with reduced amounts of other vulcanizing agents. Similar, butnot identical, results are obtained with analogous compounds having oneor more lower alkyl l to t 5 carbon atoms), lower alkoxy, halogen ornitro substituents in the benzene ring of the benzothiazole moiety, forexample, S-chloro, 4-methyl, 6-ethoxy, or 6-nitro and it will beunderstood that they are generally equivalents. I

My invention is applicable to rubber formulations containing the usualcompounding ingredients such as reinforcing pigments, fillers,retarders, antidegradants, other vulcanizing agents and otheraccelerators. The various grades of carbon blacks, silicas and similarparticulate reinforcing materials as well as clays, whiting and similarinert extenders may be present. Other vulcanizing agents are preferablysulfur vulcanizing agents which include, of course, elemental sulfur,the one most commonly used, and also include any sulfurcontainingvulcanizing agent, other than vulcanizing agents of this invention,which upon heating release sulfur in the form available to cross-linkrubber. The various forms of elemental sulfur, amine disulfides such asN,N'-dithiobis-(morpholine), amine higher sulfides and polymericpolysulfide vulcanizing agents are all examples of sulfur vulcanizingagents. Any of the retarders and prevulcanization inhibitors known torubber compounders may be present if desired, for example,N-cyclohexylthiophthalimide. Any of the antidegradants may be present,for example, dihydroquinoline antidegradants, phenolic antidegradants,or phenylenediamine antidegradants. The accelerators perform well alonebut may be used in mixtures with other accelerators.

The compounds of my invention may be used in natural and syntheticrubbers or mixtures thereof. Synthetic rubbers that may be used inpractice of this invention include cis-4-polybutadiene, butyl rubber,ethylenepropylene terpolymers (EPDM rubber), homopolymers of1,3-butadiene, homopolymers of isoprene, copolymers of 1,3-butadienewith other monomers for example, styrene, acrylonitrile isobutylene, andmethyl methacrylate. The invention applies to diene rubbers and theterms rubber and diene rubber are synonymous for the purpose of theinvention.

The amount of compound to use for accelerating vulcanization dependsupon the components in the rubber formulation. Rubber recipes are sovaried that it is impossible to define an amount of accelerator whichwould be advantageous in every instance. A compounder having knowledgeof the other ingredients and knowing the process conditions can readilyascertain the amount of accelerator needed. The amount usually is withinthe range of 0.1 to 5 parts by weight per 100 parts by weight ofelastomer, and more often within the range of 0.3v to 2 parts by weight.The preferred usage generally comes within the range of 0.5 to 1.5 partsby weight accelerator. For use of the new compounds as a vulcanizingagent, the amount will generally be larger than for use as anaccelerator and may range up to 10 parts by weight. The compounds ofthis invention are also valuable for use in combination withaccelerators previously known examples of which are diphenylguanidine,mercaptobenzothiazole, tetramethylthiuram disulfite,N-t-butyl-2-benzothiazolesulfenamide, 2,2-dithiobisbenzothiazole, zincdimethyldithiocarbamate and other guanidine, thiazole, thiuram sulfideand dithiocarbamate accelerators.

DESCRIPTION OF PREFERRED EMBODIMENTS The compounds of this inventionwhere x is one may be made by reacting 3,5-dimercapto-4-isothiazolecarbonitrile with 2-chlorobenzothiazole in the presence of ahydrogen chloride acceptor, the presence of which is convenientlyaccomplished by employing the dimercaptan in the form of its alkalimetal salt. The intermediate, alkali metal salt of 3,5-dimercapto-4-isothiazolecarbonitrile may be prepared by sulfurization of2,2-dicyano-l,l-dialkali metal mercaptoethylene. Hatchard, U.S. Pat. No.3,232,935. The compounds of this invention where x is two may be made byreacting the same intermediate with a 2- benzothiazolesulfenyl halide.

A preparation of the dipotassium derivative is as follows: A mixture of218.4 grams (1.0 mole) of 2,2- dicyanol l -dipotassiornercaptoethylene,2000. ml. of methanol and 33.6 grams (1.05 mole) ofsulfur is refluxedwith stirring for one hour. The mixture is filtered hot to remove asmall amount of solid material. The methanol is removed at the maximumtemperature of 40C. in vacuo. The solid residue is dissolved in 950 ml.of ethanol and 50 ml. of water at reflux temperature. The solution isfiltered to remove trace impurities. The solution is cooled to 0C., and300 ml. of ethyl ether and 200 ml. of ethyl acetate are added. After onehour between 0-10C., the solid product is recovered by filtering, and isair dried at 25-30C. to obtain 198 grams (79 percent yield) of3,5-dipotassiomercapto-4- isothiazolecarbonitrile. This material is usedas shown in the examples below.

EXAMPLE 1 4-Cyanoisothiazol-3,5-diyl bis( 2-thiobenzothiazole) isprepared by the following procedure. To a stirred solution of 25 grams(0.1 mole) of 3,5- dipotassiomercapto-4-isothiazole-carbonitrile(prepared above) in 200 ml. of dimethylformamide, 34 grams (0.2 mole) of2-chlorobenzothiazole is added in one portion at room temperature. Afterstirring the mixture for 18 hours at l00C., it is cooled to 30C.followed by the addition of 800 ml. of water and stirring is continuedfor 30 minutes at 25-30C. The

Stock A i B c D E Masterbatch 157 157 157 157 157 Sulfur 1.0 1.2 2.0 2.0Example 1 1.0, 0.5 Example 2 3.0 1.0 0.5

solid product is then recovered by filtration, washed with water untilneutral and air dried at 25-30C. to obtain 40 grams (90.9 percent yield)of the desired 4- cyanoisothiazol-3,5-diyl bis(2-thiobenzothiazole) as atan solid which melts at 244246C. Analysis gives 12.56 percent nitrogenand 36.12 percent sulfur compared to 12.72 percent nitrogen and 36.39percent sulfur calculated for CmHgNqSs.

EXAMPLE 2 The stocks are heated at 144C. for the length of time requiredto obtain optimum cure. Such time is obtained from curingcharacteristics determined by means of the Monsanto Oscillating DiskRheometer described by Decker, Wise, and Guerry in Rubber World,December 1962, page 68. From the Rheometer data the time to optimum cureis determined, and the stocks are heated in a press for that time which,in the case of Stocks A to E above. varies from to 90 minutes. Theultimate tensile strength and tensile modulus at 300 percent elongationare determined for each vulcanizate. Mooney scorch times at 135C. aredetermined by means of a Mooney Plastometer. The time in minutes (t,-,)required for the Mooney reading to rise five points above the minimumviscosity is recorded. Reversion is evaluated with the Rheometer at164.4C. The drop in Rheometer units after heating ten minutes beyond thetime of maximum torque is recorded. Resistance of vulcanizates toreversion is a valuable attribute.

The excellent accelerating activity of the new compounds is shown by thedata in Table I. The modulus and tensile data are in pounds per squareinch.

TABLE I Stock A B C D E Cure time, minutes 70 30 75 90 300% Modulus, psi500 1080 630 1210 880 Ultimate Tensile 1700 2810 1170 2840 2320Strength, psi Ultimate 550 550 540 530 550 Elongation, Mooney Scorch18.0 1 1.4 1 14.2 13.7 73.4 Time, (t min. Reversion 0.3 4.0 3.6 6.4 4.4

Torque units ing and is then stirred at 2530C. for 44 hours followed bythe addition of 1500 ml. of water and 25 ml. of 25 percent sodiumhydroxide solution. The resulting mixture is cooled to 0C., stirred at0l0C. for 20 minutes and filtered. The solids collected on the filterare washed with water and dried to obtain 4- cyanoisothiazol-3,5-diylbis(Z-dithiobenzothiazole) in a yield of 91 percent. After purificationby slurrying 10 grams of the product in 100 ml. of toluene for 1 hour at2530C., filtering and drying, it melts at 142-145C. Analysis gives 43.07percent carbon, 1.80 percent hydrogen, 10.91 percent nitrogen and 44.20percent sulfur compared to 42.83 percent carbon, 1.60 percent hydrogen,11.10 percent nitrogen and 44.47 percent sulfur calculated for C I-1 198 The accelerating and vulcanizing activity of the compounds of thisinvention are illustrated by incorporating them into the followingrubber recipe.

Masterbatch Parts by Weight Smoked sheets 100 Carbon black (lSAF) 45Zinc oxide 3 Stearic acid 2 Hydrocarbon softener 5 Antidegradant 2 Totalparts 157 1. A compound of the formula in which x' is one-or two.-

2. A co'mpoundof claiml in which x is one. 3. A compound of claim 1 inwhich x is two.

1. A COMPOND OF THE FORMULA
 2. A compound of claim 1 in which x is one.3. A compound of claim 1 in which x is two.